System for removing a clot from a blood vessel

ABSTRACT

A system for removing obstructions from a blood vessel comprises a clot retrieval device and a catheter. The clot retrieval device comprises a clot engaging element attached to the distal end of an elongate shaft. The elongate shaft has a shaft proximal section, a shaft distal section and a shaft intermediate section between the shaft distal and proximal sections. The catheter has a catheter proximal section, a catheter distal section, and a catheter intermediate section between the proximal and distal sections. The maximum diameter of a shaft proximal section is greater than an inner distal lumen of the catheter distal section.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/019,137, filed Jun. 30, 2014, the entirety of which is incorporatedherein by reference in its entirety.

INTRODUCTION

Acute ischemic stroke (AIS) is a worldwide problem for which untilrecently there have been only limited therapy options available forpatients. One option for such patients is a lytic drug called tPa, whichcan be administered either intravenously or intra-arterially. Morerecently various mechanical thrombectomy and/or revascularisationdevices have become available which aim to dislodge and remove the clotusing mechanical means. These devices are typically advanced through asmall catheter (called a microcatheter) to the site of the occlusiveblood clot, whereupon they are deployed from this microcatheter andengaged with the clot. It would be advantageous for the patient andphysician that this microcatheter be as flexible and small in diameteras possible, as these attributes enable the microcatheter to be advancedthrough tortuous vessel anatomies with ease without harming the vesselwalls, and also enable the microcatheter to be advanced across the clotwithout pushing the clot further distally or dislodging a portion of theclot which might embolise another vessel. However it may be challengingfor a mechanical thrombectomy and/or revascularisation device to passthrough such a small diameter microcatheter. One particular challengeinvolves the ability to push the device through the microcatheter,especially around tortuous bends in distal anatomies. Many mechanicalthrombectomy and/or revascularisation devices consist of a clot engagingelement attached to the distal end of an elongate wire or shaft. Thisshaft extends exterior of the patient and is used by the physician toadvance the device through the microcatheter to the site of theobstruction. This shaft therefore needs to be robust enough, and stiffenough, to be able to push the engaging element against significantresistance as it enters regions of tortuosity. However if the device isto be used with a very small diameter microcatheter (as is desirable)then the diameter of the shaft is limited to a size somewhat smallerthan the inner diameter of this microcatheter. This trade-off betweenmicrocatheter profile and shaft profile means that conventionalmechanical thrombectomy and/or revascularisation devices either a) arecompatible with very small diameter microcatheters but suffer fromhaving flimsy shafts which are easily damaged and cannot effectivelytransmit a push force to advance the device around significanttortuosity, or b) are fitted with sufficiently large diameter shafts tohave good robustness and pushability but are not compatible with verysmall diameter microcatheters.

It is desirable for a Thrombectomy Device (TD) to have a very lowdelivery profile in order to cross an occlusive clot easily and withoutdislodging any clot material. Most TDs are delivered through amicrocatheter, and it is the microcatheter (and typically an innerguidewire) that first cross the clot. After that the guidewire isremoved and the TD is advanced through the microcatheter. Thus it isdesirable that the TD be compatible with microcatheters that are assmall as possible in diameter. A further advantage of a small diametermicrocatheter is that increased space is available between themicrocatheter and the inner surface of a guide catheter or intermediatecatheter through which it passes. This increased space makes it easierto aspirate blood and clot from the site of occlusion through the guideor intermediate catheter, which is a method typically used inconjunction with use of a thrombectomy device. Some physicians choose toremove the microcatheter completely before aspirating in order toincrease this space and reduce the resistance to flow through anintermediate catheter, particularly if a large diameter microcatheterand/or small diameter intermediate catheter is used. It would bedesirable if such a step were not required.

It is generally necessary to have some clearance between the innerdiameter of a catheter and the outer diameter of the shaft of a devicethat is passed through it. Without any clearance the shaft would notmove freely through the catheter and would be very difficult to advance.The clearance required depends on both the internal diameter of thecatheter (its lumen) and the degree or tortuosity of the vasculature inwhich it is positioned. In relatively low levels of tortuosity a smallclearance between shaft and catheter lumen may be perfectly adequate,but in higher levels of tortuosity greater clearance may be required topermit free movement. For example, in the case of a neurovascularthrombectomy system used in middle cerebral artery via femoral access: aclearance of less than 0.003″ (ie 0.0025″, 0.002″ or even less than0.002″) may be adequate for the proximal section of the system whichsits proximal of the patients aortic arch take off, while a clearance of0.003″ or more may be required to permit free movement of thethrombectomy device shaft through the microcatheter in the section ofthe system distal of the common carotid artery.

Many TDs today are compatible with microcatheters with an inner lumen ofapproximately 0.021″ and an outer diameter of 0.025″ to 0.034″ or more.These TDs can therefore be mounted on shafts that have an outer diameterof up to approximately 0.018″ (to comfortably fit in the 0.021″ lumen).Some TDs are compatible with smaller microcatheters which have a lumenof approximately 0.016″ to 0.17″ and an outer diameter as low asapproximately 0.020″. These lower profile catheters may be more easilyadvanced into tortuous distal vessels and may cross clots more easilydue to their lower profile. However a TD that is designed to fit throughone of these catheters must have a shaft diameter of approximately0.014″ or less. The bending stiffness of a 0.014″ shaft is 63% lowerthan that of a 0.018″ shaft of the same material, because the bendingstiffness is proportional to the fourth power of the shaft diameter.Therefore the pushability of the 0.014″ shaft is also much less thanthat of the 0.018″ shaft. Thus a 0.014″ shaft would need to have a muchhigher modulus of elasticity than an 0.018″ shaft in order to deliver asimilar level of “pushability”. However it is desirable that theseshafts are made from a superelastic or shape memory material such asnitinol so that they retain their shape and do not become kinked ordeformed after use, as they may need to be reused for additional clotretrieval passes if the first is not successful. One way to attain ahigher modulus and hence recover some pushability would be to changeshaft material to stainless steel or other relatively high modulusmaterial. However this means compromising on the kink resistance anddurability of the nitinol shaft. Thus there is a need for a solution tothis undesirable trade-off problem.

The solutions provided herein are applicable not just to AIS, but alsoto the removal of obstructions from vessels throughout the body, such asperipheral arteries and veins, coronary vessels and pulmonary vesselswhere embolism can be a serious problem

STATEMENTS OF INVENTION

According to the invention there is provided a system for removingobstructions from a blood vessel, the system comprising a clot retrievaldevice and a catheter. The clot retrieval device comprises a clotengaging element and an elongate shaft; the clot engaging element havinga first collapsed delivery configuration and a second expanded deployedconfiguration. The elongate shaft has a shaft proximal section, a shaftdistal section and a shaft intermediate section between the shaft distaland proximal sections. The clot engaging element being attached to theshaft distal section of the elongate shaft. The catheter has a catheterproximal section, a catheter distal section, and a catheter intermediatesection between the proximal and distal sections. The catheter proximalsection has an inner proximal lumen and an outer proximal diameter, thecatheter distal section having an inner distal lumen and an outer distaldiameter.

In one embodiment the maximum diameter of the shaft proximal section isgreater than the inner distal lumen of the catheter distal section.

In one embodiment the maximum diameter of the shaft proximal section isless than 0.003″ smaller than the inner distal lumen of the catheterdistal section.

In one embodiment the maximum diameter of the shaft proximal section isless than 0.002″ smaller than the inner distal lumen of the catheterdistal section.

In one embodiment the maximum diameter of the shaft proximal section isgreater than the maximum diameter of the shaft distal section.

In one case the inner proximal lumen of the catheter is larger than theinner distal lumen of the catheter.

In some cases the outer proximal diameter of the catheter is larger thanthe outer distal diameter of the catheter.

In one embodiment the outer proximal diameter of the catheter is equalto the outer distal diameter of the catheter (see, e.g., FIG. 6).

The clot engaging element may be self-expandable. The clot engagingelement may comprise a self-expanding nitinol body.

The invention also provides a method for removing obstructions from ablood vessel comprising:

-   -   providing a clot retrieval device and a catheter system        according to the invention;    -   positioning a guide catheter or sheath proximal of an        obstruction in a blood vessel;    -   advancing a guidewire towards the obstruction;    -   advancing the catheter over the guidewire;    -   removing the guidewire;    -   advancing the elongate clot retrieval shaft through the catheter        with the clot retrieval element in the collapsed delivery        configuration;    -   advancing the catheter and the shaft through the obstruction;    -   deploying the clot engaging element in the obstruction;    -   retracting the catheter to a position proximal of the clot        retrieval element; and    -   retrieving the clot retrieval element and the clot captured by        the retrieval element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription of an embodiment thereof, given by way of example only, withreference to the accompanying drawings, in which:

FIG. 1a is a cross sectional side view of a clot retrieval systemaccording to the invention;

FIG. 1b is a cross sectional side view of a clot retrieval systemaccording to the invention;

FIGS. 2a to 2e are views illustrating the clot retrieval system in use.

FIG. 3 is a cross sectional side view of a portion of a clot retrievalsystem according to the invention.

FIG. 4 is a cross sectional side view of a portion of a conventionalclot retrieval system.

FIG. 5 is a cross sectional view through FIGS. 3 and 4.

FIG. 6 is a cross sectional side view of a clot retrieval systemaccording to the invention.

DETAILED DESCRIPTION

Referring to FIGS. 1a and 1b of the drawings there is illustrated asystem 24 for removing obstructions such as clot from a blood vessel,the system comprising a clot retrieval device 8 having a clot retrievalelement 7 mounted at the distal end of an elongate shaft 9 and acatheter 2 which in this case is a microcatheter which is used todeliver the clot retrieval element 7 in a collapsed deliveryconfiguration across a clot. The clot retrieval element 7 is deployedfrom the catheter 2 into an expanded deployed configuration for clotretrieval. FIG. 1a shows the system with the clot retrieval element 7 inthe deployed expanded condition. FIG. 1b shows the system with the clotretrieval element 7 collapsed within the distal portion 16 of themicrocatheter 2, just prior to deployment.

The catheter 2 comprises a catheter proximal section 15, a catheterdistal section 16, and a catheter intermediate section 6 between theproximal and distal section. The catheter distal section 16 has an innerdistal lumen and an outer distal diameter. The catheter proximal section15 has an inner proximal lumen and an outer proximal diameter. Thecatheter comprises a hub 19 at its proximal end to which is typicallyattached a rotating haemostasis valve (RHV) 20, through which fluids maybe injected or aspirated and which incorporates a seal to prevent theingress of air and loss of blood or other fluids.

The shaft 9 of the clot retrieval device comprises a shaft proximalsection 17, a shaft distal section 18 and a shaft intermediate section10 between the shaft distal and proximal sections. The clot engagingelement 7 is attached to the shaft distal section 18 of the shaft 9 atconnection point 23 and may be self-expandable. For example, the clotengaging element may be formed from or comprise a self-expanding Nitinolbody. Indicator bands 21 and 22 may be provided on the proximal shaft17, to inform the user of the proximity of the clot retrieval element 7to the distal end of the microcatheter 2.

The catheter 2 has a stepped diameter. The distal section 16 of thecatheter 2 has a low profile (for example 0.16″ inner diameter(ID)/0.020″ outer diameter (OD)) for excellent flexibility and clotcrossing capability. The proximal section 15 of the catheter 2 has alarger inner (and outer) diameter to accommodate a robust and pushableproximal shaft 17 of the clot retrieval device.

In one embodiment of the invention the maximum diameter of the shaftproximal section 17 is larger than the inner distal lumen of thecatheter distal section 16. In another similar embodiment the shaftproximal section 17 is very slightly smaller than the inner distal lumenof the catheter distal section 16, so that the catheter can becompletely withdrawn over the shaft when in a relatively straightconfiguration, while still benefiting from a robust large diametershaft.

As the catheter 2 is not typically withdrawn more than a short distanceduring use, the shaft proximal section 17 may be even larger than theinternal diameter (ID) of the distal section 16 of the catheter 2. Insome cases the shaft proximal section 17 is only slightly smaller (i.e.0.003″ or less smaller or 0.002″ or less smaller) than the ID of thedistal section 16 of the catheter 2—for example the distal section ofthe catheter may have a lumen of 0.0175″, and the shaft proximal sectionmay have an OD of 0.016″. This diameter difference allows themicrocatheter 2 to be completely withdrawn over the device shaft 9 ifdesired, provided that the larger diameter proximal portion of thedevice shaft 17 is not positioned in a region of significant tortuosity.

FIGS. 2a to 2e show a method of use of the clot retrieval system 24 ofthis invention. FIG. 2a shows a clot 1 lodged in vasculature 25 causingan obstruction to the flow of blood. A large diameter guide catheter orsheath 5 is positioned in a vessel proximal of the obstructive clot. Amicrocatheter 2 is advanced through the guide or sheath 5 towards theclot 1 with the aid of guidewire 3. A region of tortuousity existsbetween the distal end of guide or sheath 5 and the clot 1, comprisingat least one tight bend 4. Such tortuosity may comprise bends if radiiless than 10 mm and in some cases less than 5 mm, and may also comprise“figure of 8” loops and compound curves are very difficult to navigatethrough without a highly flexible microcatheter. In addition the clotitself may be difficult to cross. Hence it is advantageous to provide aflexible and low profile distal segment 16 in a microcatheter such asthat of this invention, which also comprises a supportive and robustproximal section 15 with which to advance the catheter through thechallenging region of tortuousity and across the clot. The length of thedistal low profile, flexible section 16 is at least long enough suchthat only this low profile section reaches the clot 1, and mostpreferably such that only this low profile section reaches the region oftortuousity distal of the guide or sheath 5. For treatment of AIS thiscatheter section is therefore ideally at least 5 cm in length and ismost preferably between 10 cm and 30 cm in length. In other embodimentsthe distal section 16 may extend to as much as 100 cm or more, whichwill provide the benefit of increased luminal space for aspirationwithin an intermediate catheter (if used), but at the cost of somepushability performance of the microcatheter.

Once the microcatheter has been successfully advanced across the clot 1,the guidewire 3 is removed as shown in FIG. 2b , so that clot retrievaldevice 8 can be advanced through the lumen of the microcatheter 2towards the target clot as shown in FIG. 2c . The microcatheter 2 isthen retracted to allow the clot retrieval element 7 to expand withinand grip the clot 1 as shown in FIG. 2 d. The distal shaft section 18ideally has a longer length than the distal microcatheter section 16, sothat the microcatheter can be retracted to a position proximal of theclot retrieval element as shown in FIG. 2d . As with the microcatheter,the larger diameter and stiffer proximal section 17 of the clotretrieval device shaft provides the shaft with greater pushability thanwould be the case with a lower profile shaft, enabling the user toadvance the device more easily through the challenging region oftortuosity distal of the guide or sheath 5, and around tight bend 4.

Once the clot retrieval element 7 has been deployed within the clot itmay be left for a few minutes to expand and embed within the clot or itmay be withdrawn immediately according to the physicians preference. Ineither case the clot and retrieval element may be withdrawn directlyback into guide or sheath 5, or an intermediate catheter 11 may be usedin a “tri-axial” set-up as shown in FIG. 2e . Aspiration though theguide/sheath and/or intermediate catheter is typically used to assist increating a reversal of blood flow and safely retrieving back the clotand any clot fragments that may be liberated. This aspiration can beapplied by means of a syringe or vacuum pump connected to the proximalend of the intermediate catheter. If this aspiration is applied throughan intermediate catheter the space within the lumen of this catheter hasa significant impact on the flow rate that can be created for a givenaspiration force. As a maximum of 1 atmosphere vacuum can be created bya syringe or vacuum pump the luminal space is a critical factor inoptimising the effect of this vacuum on flow rate.

FIG. 3 shows a simplified view of a cross section through a systemincorporating an intermediate catheter 11 as shown in use in FIG. 2e .The intermediate catheter 11 may have a stepped profile as shown with alarge lumen in proximal section 13 than in distal section 12, or inother embodiments may have a constant inner diameter. The distal luminalspace 30 and proximal luminal space 31 are the areas between the outersurface of the microcatheter 2 and the inner surface of the intermediatecatheter 11 through the aspiration force is applied. The effective flowrate through such a system is a function of the cross-sectional areasand lengths of spaces 30 and 31, and the viscosity of the fluid inquestion (which is blood). Thus it is advantageous to maximise thecross-sectional areas and minimize the lengths of spaces 30 and 31.

FIG. 4 shows a simplified view of a cross section through a conventionalthrombectomy system incorporating an intermediate catheter 52, amicrocatheter 53 with a continuous non-stepped inner lumen, and a clotretrieval device shaft 51. Comparing FIGS. 3 and 4 it can be seen thatthe system of this invention depicted in FIG. 3 has a much larger distalluminal space 30 than the distal luminal space 60 provided by theconventional system of FIG. 4. This provides a major advantage in thatwith the system of this invention aspiration can be very effectivelyapplied without the need to remove the microcatheter from the patient.Removal of the microcatheter can be both time consuming and difficult asthrombectomy device shafts are not typically long enough to permit thisto be done without the addition of an extension piece to the shaft.

FIG. 5 shows a cross-sectional view representative of that through thesystems of both FIG. 3 and FIG. 4, where clot retrieval shaft 82 lieswithin microcatheter 81, which in turn sits within the lumen ofintermediate catheter 80, leaving luminal space 83 between the two foraspiration.

The invention enables clot retrieval devices with robust and pushableshafts to be used in conjunction with flexible, small diametermicrocatheters, and enables aspiration forces to be effectivelytransmitted through an intermediate or guide catheter without the needfor removing the microcatheter.

The clot retrieval device may, for example, be of the type described inour US2013/0345739A or US2014/0371779A the entire contents of which areincorporated herein by reference.

The invention is not limited to the embodiment hereinbefore described,with reference to the accompanying drawings, which may be varied inconstruction and detail.

The invention claimed is:
 1. A system for removing a clot from a bloodvessel, the system comprising: a catheter being capable of moving withinthe blood vessel and having a lumen extended therethrough, the cathetercomprising: a catheter proximal section with a proximal section lumendiameter, a catheter distal section with a distal section lumendiameter, wherein the proximal section lumen diameter is greater thanthe distal section lumen diameter, and a catheter intermediate sectiontapered between the catheter proximal section and the catheter distalsection; wherein the proximal section lumen diameter of the catheter islarger than the distal section lumen diameter of the catheter; and aclot retrieval device comprising: a clot engaging element having a firstcollapsed delivery configuration and a second expanded deployedconfiguration; and a shaft being advanceable through the lumen of thecatheter to obstructions of the blood vessel, the shaft comprising: ashaft proximal section; a shaft distal section permanently attached tothe clot engaging element, wherein the shaft distal section is capableof crossing the clot; and a shaft intermediate section distal of theshaft proximal section and tapered between the shaft distal section andthe shaft proximal section; wherein an outer diameter of the shaftproximal section is greater than an outer diameter of the shaft distalsection; wherein the shaft proximal section outer diameter is greaterthan an inner diameter of the catheter distal section thereby inhibitingthe shaft proximal section from distally advancing through the catheterdistal section; wherein an outer diameter of the catheter proximalsection is equal to an outer diameter of the catheter distal section;and wherein the intermediate and distal sections of the catheter andshaft are advanceable through the blood vessel towards the clot.
 2. Asystem as claimed in claim 1 wherein the shaft proximal section diameteris 0.003″ or less smaller than the inner diameter of the catheter distalsection.
 3. A system as claimed in claim 1 wherein the shaft proximalsection is stiffer than the shaft distal section.
 4. A system as claimedin claim 1 wherein the catheter proximal section is substantially robustand the catheter distal section is substantially flexible.
 5. A system,comprising: a shaft having a proximal section with a proximal sectiondiameter and a distal section with a distal section diameter, whereinthe distal section tapers so that the distal section diameter is smallerthan the proximal section diameter; an expandable clot engaging elementpermanently fixed to the distal section of the shaft; a first catheterhaving a first catheter proximal section and a first catheter distalsection, wherein the first catheter includes a lumen extendingtherethrough, wherein the first catheter distal section tapers so thatthe first catheter proximal section has a proximal section lumendiameter larger than a distal section lumen diameter, wherein an outerdiameter of the first catheter proximal section is equal to an outerdiameter of the first catheter distal section; and a second catheteraxially aligned with the first catheter, at least a portion of the firstcatheter advanceable within a lumen of the second catheter; wherein theshaft is distally advanceable within the first catheter and the secondcatheter; wherein the proximal section diameter of the shaft is greaterthan the distal section lumen diameter of the first catheter distalsection thereby inhibiting the shaft proximal section from distallyadvancing through the catheter distal section.
 6. A system as claimed inclaim 5 wherein the second catheter has a lumen extending therethrough,wherein the lumen of the second catheter has a diameter larger than anouter diameter of the first catheter proximal section.
 7. A system asclaimed in claim 5 wherein the shaft further includes a radiopaqueindicator.
 8. A system as claimed in claim 5 wherein the second catheterincludes a second catheter proximal section and a second catheter distalsection, wherein an outer diameter of the second catheter proximalsection is larger than an outer diameter of the catheter distal section.9. A method for using the system of claim 1, comprising: advancing theclot engagement element, by distally advancing the shaft through thecatheter, extending the catheter across an obstruction in a bloodvessel, retracting the catheter so as to expand and deploy the clotengagement element distal of the catheter within the obstruction; andretrieving the clot engagement element and the obstruction from theblood vessel.
 10. A method as claimed in claim 9 further includingadvancing a guidewire across the obstruction and through the catheter,and, removing the guidewire from the catheter after advancing thecatheter.
 11. A method as claimed in claim 10 further includingmaximizing a distal luminal space defined between the shaft distalsection and the catheter distal section.
 12. A method as claimed inclaim 9 wherein the shaft proximal section is stiffer than the shaftdistal section, and wherein the catheter proximal section is robust andthe catheter distal section is flexible.
 13. A method as claimed inclaim 9 wherein the catheter is a first catheter, the method furtherincluding advancing a second catheter to a first location proximal ofthe obstruction, and advancing a guide catheter to a second locationproximal of the obstruction, wherein the retrieving includes withdrawingthe clot engaging element into a lumen of at least one of the secondcatheter or the guide catheter.